Hyperthermia is the heating of living tissue for therapeutic purposes. Hyperthermia has been used as a method of treating cancer by means of raising the temperature of a tumor locally, or a region of the body in which the tumor is located, or of the whole body. It has long been known that high heat can trigger the natural regression and/or remission of tumors. Because of its effect on cancer cells, hyperthermia may be used as an independent therapy or in conjunction with other cancer therapies, such as radiation, surgery, chemotherapy, and immunotherapy to enhance the effectiveness of these therapeutic modalities. Current hyperthermia techniques used in cancer therapy include regional perfusion with heated fluids, microwave heating, fluid emersion, low frequency (RF) current fields, and ultrasound.
Three of the most common types of currently used hyperthermia techniques involve radio frequency, microwaves and ultrasound. Radio frequency and microwave equipment may be used for local, regional and whole body heating. Ultrasound can also be used for local and regional heating.
Microwave hyperthermia systems have been developed utilizing direct contact microwave waveguide applicators. The depth of penetration of the microwave energy is frequency-dependent and the penetration is also a function of tissue, anatomical structure and blood flow dynamics. The design of the microwave waveguide applicator has direct impact on the thermal patterns in human body tissue. In addition, sharp changes in patient contour within the heated area, as in the head and neck region, will have an influence on the thermal distribution. In some microwave hyperthermia treatment systems microwave power from a microwave generator can be transmitted to the load (human tissue) through a direct contact microwave applicator. Such microwave hyperthermia treatment systems further include control instrumentation. A frequency counter may be connected to a directional coupler for microwave frequency measurements. A power meter may be connected to a forward power port of a dual directional coupler for forward power measurements. A power meter may also be connected to a reflected power port of a dual directional coupler for reflected power measurements from a microwave applicator. In order to obtain a good efficiency of microwave energy transmission from a microwave energy generator to human tissue, reflected microwave power from the load should be minimized. Reflected microwave energy from the load may be minimized by tuning the frequency of the applicator and/or tuning the coupling of the microwave power to the applicator.
Prior art microwave direct contact applicators have been designed at only single or dual operating frequencies. These applicators can be adjusted within only a very narrow frequency range with a tuning device of some kind. Microwave input power coupling is typically used, such as either an adjustable or fixed antenna stub. The antenna stub is a part of applicator design and is installed in a region of maximum electric field which is located at one quarter waveguide wavelength from the closed end of the applicator along the applicator axis. Since the position of the maximum electric field changes rapidly with frequency, a required input coupling is provided only within a narrow frequency range at the design frequency. The second frequency is usually of an arbitrary value. In typical hyperthermia systems of the prior art, the microwave applicator had an adjustable antenna stub installed in a region of maximum electric field at one quarter waveguide wavelength from the closed end of the applicator along the applicator axis. A tuning device operated to adjust the frequency within a very narrow frequency range. The microwave applicator was designed only for a single operating frequency with very narrow frequency adjustments provided by the tuning device. In some cases, a second operating frequency of arbitrary value could be obtained. A typical prior art cylindrical waveguide direct contact microwave applicator of present systems operates at a frequency of 433 MHz. Since the position of the maximum electric field changes rapidly with changes in frequency, the required input coupling is provided only within a very narrow frequency range of the design frequency.
Microwave applicators have been developed which have attachments on the top, bottom, or sidewalls for making tuning adjustments for the applicator. The placement of such attachments have proven to be undesirable in multiple applicator configurations in which the applicators are positioned closely to each other in an array with varying angles of separation between adjacent applicators to optimize the heating pattern in the treatment area.
Microwave applicators have been used with various cooling systems to reduce the heat produced by the applicator at the surface of the treatment area. Water cooling belts have been located between the applicator and the surface treatment area to circulate cool water through the belt to carry off some of the surface heat. Cool air has also been forced by blowers in the space between the face of the microwave applicator and the surface of the treatment area.
A need has thus arisen for a microwave applicator having discoupled frequency and input power coupling tuning over a broad range to provide microwave matching over a broad range of microwave loads in a clinical environment, including multiple applicator modality, which usually involves microwave interaction among applicators, especially incoherent modality of operation. A need has also arisen for having all the tuning functions, including RF connectors, located behind the closed end of the applicator in the applicator's cross sectional geometry for facilitating the arrangement of an array of applicators. A need has also arisen for operating a microwave applicator in a direct or indirect contact mode of operation, where the input power coupling is adjustable over a broad range of clinical microwave load conditions. A need has also arisen to reproduce a microwave applicator input coupling and frequency tuning setting for a prescribed course of clinical treatment, especially for operation of multiple microwave applicators.